Corrosion control

ABSTRACT

A PROCESS FOR CONTROLLING CORROSION IN SWEET (HYDROGEN SULFIDE FREE) ENVIRONMENTS COMPRISING A TREATMENT OF THE ENVIRONMENT IN WHICH CORROSION IS TO BE CONTROLLED WITH NORMALLY CORROSIVE SOURING AGENTS IN THE PRESENCE OF ELECTROLYTE AND PREFERABLY IN THE PRESENCE OF AT LEAST ONE CONVENTIONAL CORROSION INHIBITOR. OPTIONALLY, THE SWEET ENVIRONMENT CAN BE PRE-TREATED WITH THE SOURING AGENT, OR MIXTURES OF THE SOURING AGENT AND THE ELECTROLYTE AND THEREAFTER WITH CORROSION INHIBITOR.

United States Patent 01 3,687,608 Patented Aug. 29, 1972 lice 3,687,608 CORROSION CONTROL Alfred C. Nestle, Houston, Tex., assignor to Texaco Inc., New York, N.Y. No Drawing. Filed July 24, 1970, Ser. No. 58,194 Int. Cl. C23f 11/14, 11/18 US. Cl. 212.5 5 Claims ABSTRACT OF THE DISCLOSURE A process for controlling corrosion in sweet (hydrogen sulfide free) environments comprising a treatment of the environment in which corrosion is to be controlled with normally corrosive souring agents in the presence of electrolyte and preferably in the presence of at least one conventional corrosion inhibitor. Optionally, the sweet environment can be pre-treated with the souring agent, or mixtures of the souring agent and the electrolyte and thereafter with corrosion inhibitor.

This invention concerns a process for controlling the corrosion of metal substrates in contact with a sweet environment by treating the sweet environment with substances normally corrosive to said metal substrates More particularly, this invention relates to treatment of sweet production, sweet crudes and sweet brine with souring agents, especially sulfide ion releasing agents, in the presence of electrolyte, preferably in the presence of at least one corrosion inhibitor to effect corrosion control of ferrous type metals subject to corrosion in a sweet environment.

Corrosion problems in the production and refining of crude petroleum products are traditionally classified and treated according to whether a hydrogen sulfide containing crude (sour) or hydrogen sulfide-free crude (sweet) is being produced.

It has been known for many years that sulfides in an acidic environment will corrode ferrous metal surfaces to form metal sulfides. This corrosion is manifested by pitting, scaling, blistering and the like. While corrosion induced by a sour environment is severe, it can be controlled fairly readily by the addition of conventional corrosion inhibitors to the environment. In contrast, while corrosion caused by a sweet environment is initially milder, it is more diflicult to control through the use of inhibitors and it can result in severe metal loss over extended periods of time.

Recently it has been discovered that by treating the sweet environment (in contact with ferrous metal substrates normally subject to corrosion in that sweet environment) with souring agents in conjunction with electrolytes and optional conventional corrosion inhibitors, the extent and severity of corrosion in the metal substrates is significantly reduced. Not only is corrosion inhibited but the quantity of inhibitor ordinarily required for long-term corrosion control is substantially reduced. Inasmuch as souring agents and electrolytes have long been considered within the art as corrosion initiators and corrosion accelerators for ferrous metals and their alloys, it was most unusual to find that the combined effect of both of these ordinarily corrosive substances would substantially improve the long-range corrosion control at lower application levels of inhibitors.

While the mechanism of how improved corrosion control is effected is presently unknown, and while no mechanism is relied upon for patentability, it is known that the treatment of the sweet environment in contact with the metal substrate to be protected, with a souring agent in the presence of electrolyte temporarily creates a sour environment. It is postulated that this temporary sour environment is conducive to the formation of a thin sulfide film upon the metal substrate. This protection against corrosion aiforded by the film is believed to be further increased by the addition of conventional corrosion inhibitors either concurrent with or subsequent to the treatment with souring agent and electrolyte. The result of this novel method of treatment is enhanced longterm corrosion control at reduced costs. That this novel treatment would function in this manner is most surprising and could not have been anticipated based upon the state of the art.

In view of the above, it is a broad object of this invention to provide a novel process to improve corrosion control in ferrous metal type substrates in contact with sweet production environments which are normally subject to corrosion in said sweet environments.

It is another object of this invention to provide a corrosion controlling concentrate which when used in conjunction with conventional corrosion inhibitors reduces the quantity of said inhibitors required for extended corrosion control and/or enhances their effectiveness.

Additional objects will suggest themselves to those skilled in the art after a reading of this disclosure.

In practice, the corrosive attack of a sweet production environment in contact with a ferrous metal type substrate is controlled by treating the sweet environment, in the presence of electrolyte, with a quantity of souring agent sufficient to temporarity convertthe sweet environment to a sour environment until corrosion control in said substrate is obtained. This corrosion controlling treatment may be renewed for extended periods of time by renewed treatments with one or more of the treatment components.

In the preferred practice, improved, long-term corrosion control of ferrous metal type substrates in contact with a corrosive sweet production environment such as is found in sweet crude oil and gas production environments, is achieved by treating said sweet environment, in the presence of electrolyte and at least one conventional corrosion inhibitor, with suflicient sulfide ion releasing agent to temporarily convert said sweet environment to a sour environment until improved corrosion control is obtained. Again renewed treatment can be given; as described above.

In order to aid in the understanding of the inventive concept, the following additional disclosure is submitted.

(A) Souring agents: These are the substances used to convert the normally sweet production environment to a temporarily sour environment. As indicated earlier, the souring agents are used in conjunction with electrolytes, natural or synthetic, preferably in the presence of conventional corrosion-inhibiting agents. The souring agent preferred is hydrogen sulfide with naturally sour crude oils also being favored. Additional souring agents which may be used include agents which release the sulfide ion under acidic conditions. These are typified by sodium and potassium sulfides among others.

The souring agents are used in amounts sufiicient to temporarily convert the sweet environment which is in contact with the metal to be protected, to a sour environment. The amount of souring agent required to go from sweet to sour cannot be stated precisely, because of numerous empirical variables involved. These include the souring agent used, the characteristics of the sweet environment treated, the conventional inhibitor employed as the supplementary protective agent, as well as the type of equipment being protected. However, where hydrogen sulfide is used as the souring agent in the presence of electrolyte and a conventional corrosion inhibitor, significant corrosion control has been obtained in the equipment, flowlines, heat exchangers, etc., when as little as 1000 p.p.m. of hydrogen sulfide has been present. Of course,

higher concentrations of souring agent may be employed without detriment, the upper concentration limit really being determined by cost and to some extent by the solubility of the souring agent in the application media. Where hydrogen sulfide is the souring agent used, it may be applied directly into the equipment or its locus in the sweet environment. However, it is usually more convenient to apply the hydrogen sulfide dissolved in the form of an aqueous, aqueous-oil mixture or oil media. When Water is employed as much as 1000 to 3000 or more p.p.m. of hydrogen sulfide can be contained in the application media while most oils permit concentrations up to about 5200 p.p.m. of sulfide in the application media.

(B) Time required for corrosion control to take place upon the metallic substrate: The time required for corrosion control which is believed to be substantially derived from the formation of a sulfide film or sulfide coating upon the surface of the metal surface is a variable, depending upon several factors. These include the type and surface area of the metal to be protected, the type of souring agent and the concentration employed and the characteristics of the particular sweet environment treated. In laboratory evaluations of the type described, see column 4, protection, presumably from film formation, has been obtained in times as short as several minutes when synthetic brines containing upwards of 1000 p.p.m. of hydrogen sulfide are used as souring agent. Naturally, in field work where equipment possessing relatively large surface areas (such as flow lines or heat transfer devices) are to be protected, corrosion control can take much longer, that is, several hours or more. Inasmuch as the anti-corrosive protection alforded by the inventive treatment is for periods of time ranging from months to a year or more, the time required to obtain corrosion control is not critical.

(C) Electrolyte: As used throughout this application, the word refers to relatively concentrated solutions of acidic ionizable salts, predominantly halides which are used in conjunction with the souring agents. These salt solutions can be of natural or synthetic origin and usually comprise the alkali metal halides such as sodium chloride and may include, in addition, alkali metal halides such as calcium chloride. These halide solutions preferably are aqueous solutions having a concentration ranging from about 5% by weight up to about 11% by weight of soluble metallic chloride. These solutions may be applied concurrently with, prior to, or subsequent to the application of souring agent to the sweet production environment. Mechanical or manual means of application may be employed. When the souring agent is hydrogen sulfide, a souring agent relatively soluble in water or water-oil mixture, it is preferred to saturate the aqueous brine mixture or an oil-containing brine mixture with hydrogen sulfide and apply them together to the equipment to be protected in the corrosive sweet environment. While the concentration of metallic chloride does not appear to be critical to operability, the best results have been obtained at concentrations of chloride not much higher than 11 to 12% by weight of metallic chloride. Useful natural brines include naturally sour production areas, either diluted or enriched as desired. A convenient aqueous synthetic brine solution which has been employed comprises by weight of sodium chloride and 0.5% by weight of calcium chloride containing from about 1000 to 3000 p.p.m. of hydrogen sulfide. As indicated above, the addition of oils to these synthetic or natural brine solutions increases the capacity of the solution for hydrogen sulfide.

(D) Conventional corrosion inhibitors: Insofar as can be determined, the choice of inhibitor is not critical. For the purposes of this invention any one of the many commercially available corrosion inhibitors can be used. Three typical inhibitors appear as follows:

4 Corrosion Inhibitor A Component: Parts by weight Oleic acid 14.4 Octadecyl amine 13.7 Isopropyl alcohol 10.0 Xylene 61.9

Corrosion Inhibitor B Component: Parts by weight Fatty amido diamine 11.0

Free fatty acids 3.0 Sulfonic acid 3.0 Isopropyl alcohol 10.0 Aromatic solvent 73.0

Corrosion Inhibitor C Component: Parts by weight l-aminoethyl-Z-imidazoline with an unsaturated C-17 alkyl group 12.2

Polyoxyethylene lauryl ether 0.8

High molecular weight containing dimer and trimer acids 15.2

Aromatic solvents 71.8

The concentration of inhibitors to be employed in conjunction with souring agent and electrolyte usually is found to be significantly less than the manufacturers recommended application level. Again, precise statements as to limits are difiicult to make but, when synthetic brine containing upwards of 1000 p.p.m. of hydrogen sulfide are employed, as little as 0.02% by weight concentrations of any of the three inhibitors have been successfully employed.

(E) Ferrous type metal substrates: This is the generic term employed to describe the metal equipment in which corrosion is to be controlled. The equipment can be of various shapes and sizes of tubular or solid construction and includes fiowlines, heat exchangers, cooling towers and the like. The sole limitations are that they are in contact with a sweet environment and that the material that they are fabricated from is iron, or an iron based alloy normally corrosive to said sweet environment. These iron based alloys include mild steels of a non-stainless type.

(F) Testing procedure: In order to evaluate the inventive process two testing procedures are employed, the first being a simulated field usage laboratory test and the second being an actual field trial.

(1) Simulated field usage laboratory test-Weighed mild steel shim stock coupons 3 x 0.4 x 0.005 inches are first exposed in a bottle to a sour solution for ten minutes while rotating on a wheel, in a thermostatted oven set at 120 F. The sour solution is made up by mixing 10 ml. of refined 300 oil, 1 m1. of 6% by weight of acetic acid and ml. of brine made from distilled water containing 10% by weight sodium chloride and 0.5% by weight calcium chloride, and gassing with hydrogen sulfide for five minutes. Coupons are removed from the sour solution and transferred to bottles containing fresh sweet fluids made up by mixing 10 m1. of refined 300 oil, 1 ml. of 6% by weight of acetic acid and 90 ml. of brine made from distilled Water containing 10% by weight sodium chloride and 0.5% by Weight calcium chloride, and 0.2% by weight of 'a corrosion inhibitor, gassing with carbon dioxide for five minutes. The bottles are placed on a wheel in a thermostatted oven set at F. and rotated at 30 r.p.m. for an hour. At the end of the hour the coupons are removed from the sweet filming solution and transferred to bottles containing fresh sweet fluids made up by mixing 10 ml. of refined 300 oil, 1 ml. of 6% by weight of acetic acid and 90 ml. of brine made from distilled water containing 10% by weight sodium chloride and 0.5 by weight of calcium chloride and gassing with carbon dioxide. The bottles containing the fresh uninhibited fluids are rotated at 30 r.p.m. for an hour on a wheel in a thermostatically controlled oven set at 120 F. At the 1 Corrosion Inhibitor C, Whose composition appears in this column.

end of the hour the coupons are removed from the sweet rinse solution and transferred to bottles containing fresh sweet fluids made up by mixing ml. of refined 300 oil, 1 ml. of 6% by weight of acetic acid and 90 ml. of brine made from distilled water containing 10% by weight sodium chloride and 0.5% by weight of calcium chloride and gassing with carbon dioxide. The bottles containing the fresh uninhibited fluids are rotated at rpm. for 72 hours on a wheel in a thermostatically controlled oven set at 120 F. At the end of the 72 hours exposure, the coupons are cleaned and weighed and the weight changes noted are used to calculate the corrosion rate in mils per year according to the text on page 633, Speller, in his book Corrosion Causes and Prevention, 3rd edition, Mc- Graw-Hill Book Company.

For the sake of establishing the value of the inventive temporary scouring procedure, the following alternate procedure is employed. The same number of weighed, mild steel coupons as before are immersed for one hour in in- Treatment and exposure sequence and times 6 rosion inhibitors through the equipment so that corrosion protection can be quickly and uniformly applied. In other equipment, the treatment is made as proximate to the equipment as it practical so that contact with the souring agent, electrolyte and optional corrosion inhibitor is made most effectively and rapidly as possible.

EXAMPLE I Simulated field usage evaluation TABLE I Corrosion rates in mils per year, metal loss in mg. and percent protection No inhibitor 0.2% by wt. inhibitor (a) To sour brine for 10 minutes (rinse step).

fiilids roi 1 hi. uninhibited 6.8 m.p.y., 17 mg... 0.8 m.p.y., 1.5 mg.

29.2% protection 91.7% protection.

(d) Then to sweet simulated Well fluids for 72 hrs. uninhibited (exposure step).

(A) To sweet simulated fluids for 1 hr. inhibited or uninhibited (filmed if inhibited) (B) Then to sweet simulated well fluids for 1 hr. uninhibited (rinse step).

(C) Then to sweet simulated well fluids for 72 hrs. uninhibited (exposure step).

*Mils per year.

hibited sweet fluids made as described above and rotated at 120 F. in a filming stage. The coupons are removed and transferred to fresh sweet fluids made up as above, but uninhibited, and the bottles containing them are rotated for an hour in a rinse step at 120 F. The coupons are then removed and transferred to fresh sweet fluids made up as above, and uninhibited, and the bottles containing them are rotated for 72 hours in an exposure step at 120 F. At the end of the 72 hour exposure step the coupons are cleaned and weighed and the weight changes so determined used to calculate corrosion rate as explained above.

Control runs are made repeating the two types of runs made above, but without any inhibitor being present in the filming stage to determined the uninhibited corrosion rates with and without the preliminary souring step.

Again, corrosion rates are determined from the weight of metal lost as explained above.

(2) Field trials-weighed mild steel rods -inch diameter x 1% inches long are placed in a flow line from a naturally sweet well. In one instance a pretreatment is made with a sweet brine that produced A grade oil containing a measured amount of a commercially obtained corrosion inhibitor previously referred to as Corrosion Inhibitor (B). In the other instance pretreatment was made using a sour brine (produced with a sour B grade oil) containing the identical concentration of the B inhibitor. After the same period of exposure, the coupons were rinsed, dried and weighed to determine corrosion penetration rate in mils per year.

(G) Method of treatment: Where the shape of the metal equipment is tubular, cylindrical, or otherwise hollow in form, and the contact of the sweet environment with the equipment is internal, the treatment can be made directly to the equipment. Illustrative equipment of this type includes casing, flow lines, boilers, heat exchangers and the like. In situations such as these, it is desirable to circulate the souring agent, electrolyte and optional cor- 1.2 m.p.y., 3 mg.,

9.6 m.p.y., 24 mg.,

87.5% protection.

0.0% protection. (Control) As the above data presented in Table I establishes, an even more substantial enhancement in corrosion control is obtained when the temporary souring pretreatment is combined with use of inhibitor. Inhibitor with sweet brine gives substantially poorer results whereas the control (substrate in the sweet environment in the absence of inhibitor) gives the poorest control.

EXAMPLE II Additional simulated field trials of the inventive process Using the procedure described in Example I, additional trials are run identical to those in that example, except that in separate runs corrosion inhibitors, previously designated as Corrosion Inhibitor B and Corrosion Inhibitor C are substituted for Corrosion Inhibitor A" on a weight by weight basis. In both instances corrosion control comparable to that obtained using Corrosion Inhibitor A is obtained.

EXAMPLE III Field trials of the inventive process Using the procedure previously described under Field Trials, evaluation runs are made as follows: Previously weighed mild steel rods whose dimensions are 7 diameter x 1%" long, are exposed to fiow lines connected to wells producing a sweet A grade crude oil. Immediately after setting the rods in place, one set of rods is treated with 2 /2 gallons of Inhibitor C, dispersed in 10 gallons of sweet brine. This concentration of inhibitor is in excess of 0.1% by weight when measured vw'thin 10 minutes of treatment. A second set of rods is treated in an identical fashion also using Inhibitor C except that the 2 /2 gallons of Inhibitor C is dispersed in 10 gallons of naturally sour brine. At the end of 4 weeks and 6 weeks exposure, both sets of rods are removed, washed, dried and weighed to determine metal loss. Table II shows the results obtained.

TABLE II Corrosion penetration rate, mils per year Sweet brine Sour brine containing containing Exposure time of rods inhibitor inhibitor 4 weeks 1. 2 O. 2 6 Weeks 0. 2 0. 1

As the above data indicates, rods pretreated with the preferred system (sour diluent electrolyte containing inhibitor) gives enhanced corrosion control compared to sweet brine containing no souring agent and the identical concentration of inhibitor.

In view of the above results the novel treating method can be seen to be advantageous over the prior art corrosion processes which rely on the application of conventional inhibitors alone. The invention is further advantageous in that it utilizes readily available and inexpensive materials, and provides good, long-term protection against corrosion. Further, the method of treatment can be renewed.

The results obtained in the use of the inventive concept are both surprising and unexpected in that they utilize two materials which, according to the art, initiate and accelerate corrosion in metal substrates, rather than arresting or controlling corrosion. Yet as the data obtained demonstrates, actually enhanced protection against corrosion is obtained using the inventive concept.

The limits and bounds of the inventive concept are best ascertained by a reading of the claims which follow taken in conjunction with the instant specification.

What is claimed is:

1. A method of improving the corrosion resistance of ferrous type surfaces which normally corrode when in 3 contact with non-acidic petroleum production environments free from hydrogen sulfide, comprising adding to said enviroment (a) at least 1000 ppm. of hydrogen sulfide,

8 (b) sufiicient soluble metallic chloride to bring the concentration of said chloride in said environment up to from about 5% to 11% by weight, and (c) at least 0.02% by weight of an anti-corrosive 5 formulation whose active ingredient is selected from the group consisting of alkyl amine, fatty amido diamine and 1-amino-lower-alkyl-2-imidazoline, to improve the corrosion resistance of the ferrous type surface in said production environment.

10 2. The method of claim 1 wherein the soluble metal chloride is selected from calcium chloride, sodium chloride and mixtures of calcium chloride and sodium chloride.

3. The method of claim 2 wherein a fatty amido diamine is the active ingredient of the anti-corrosive formu- 15 lation and the soluble metal chloride is sodium chloride.

4. The method of claim 2 wherein octadecyl amine is the active component of the anti-corrosive formulation and the soluble metal chloride is sodium chloride.

5. The method of claim 2 wherein l-aminoethyl-Z-imid- 20 azoline is the active component of the anti-corrosive formulation.

References Cited UNITED STATES PATENTS 5 BARRY S. RICHMAN, Primary Examiner US. Cl. X.R. 

